1. Field of the Invention
The present invention relates to an electrophotographic member and a process cartridge used in an electrophotographic image forming apparatus (hereinafter referred to as the electrophotographic apparatus), and the electrophotographic apparatus.
2. Description of the Related Art
A large number of charging apparatuses used in electrophotographic apparatuses employ a contact charging method in which a surface of an electrophotographic photosensitive member is charged by applying a voltage to an electrophotographic member, namely, a charging member, disposed in contact with or close to the surface of the electrophotographic photosensitive member. In this method, a DC voltage alone or a voltage in which an AC voltage is superimposed on a DC voltage is generally applied to the charging member.
In order to stably conduct the contact charging, a conductive agent for adjusting conductivity is included in the charging member. Examples of the conductive agent include electron conductive agents such as carbon black and ion conductive agents such as quaternary ammonium salt.
If the charging member used in the contact charging is left to stand in a state in contact with an electrophotographic photosensitive member for a long period of time, deformation that cannot be easily recovered, namely, what is called compression set (hereinafter referred to as the “C set”) is caused in a contact portion of the charging member in contact with the electrophotographic photosensitive member.
If the charging member is left to stand in an environment of high temperature and high humidity, the degree of the set becomes more serious. When the ion conductive agent is used as the conductive agent for the charging member, the ion conductive agent is unevenly distributed in a portion having the C set (hereinafter referred to as the “C set portion”), and hence, an electric resistance value of the C set portion is varied. As a result, there arises a difference in the electric resistance value between the C set portion and a non-C set portion.
Due to differences between the C set portion and the non-C set portion in the degree of the set and in the electric resistance value, a difference is caused in charging performance of the charging member. As a result, an electrophotographic image having striped unevenness in a position corresponding to the C set portion (hereinafter referred to as the “C set image”) can be sometimes caused.
Japanese Patent Application No. 2006-189894 and Japanese Patent Application No. H07-121009 describe examples of a charging member including a polymer having a special quaternary ammonium salt or quaternary ammonium base.